Rhinichthys osculus nevadensis

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General Information

Common Name:

Amargosa Canyon speckled dace

FID:

CRO06

Status:

Class 1. Endangered listing recommended. Amargosa Canyon speckled dace are highly vulnerable to extinction in their native range in the next 50 years, because they are restricted to a single desert stream system which is under constant threat of dewatering, and is heavily invaded by alien fishes. They have not been recorded since 1982.

Life History:

Speckled dace typically form small feeding aggregations. They are omnivorous; their dietary range includes aquatic and terrestrial insects, other invertebrates, such as snails and microcrustaceans, and filamentous algae (Moyle 1976). In stream systems they are active throughout the year, including the winter months. As a consequence, because growth is continuous throughout the year they are difficult to age by scale analysis. However, length-frequency analysis of dace from various localities suggests that they may live for 5-6 years (Moyle 2002). For a general life history of the speckled dace see the Santa Ana speckled dace account in this report and Moyle (2002).
In Amargosa Canyon, the most frequent size class in May was 52-54 mm TL, but in July smaller fish averaging 31-33 mm were more common (Williams et al. 1982). However, in May there were many small fish (

This population is confined to the Amargosa River in Amargosa Canyon and tributaries to it, especially Willow Creek and Willow Creek Reservoir (Williams et al. 1982). Historically, it was found in a warm spring just north of Tecopa (Miller 1938) but that population is no longer present. Overall, its range has probably been reduced somewhat, but the exact extent is not known.

Abundance Trends:

During a 1981 survey of the Amargosa Canyon that included the river and Willow Creek, speckled dace comprised 1% of the fishes collected (Williams et al. 1982). Introduced western mosquitofish (Gambusia affinis) comprised 40% of the fish collected. This indicates that the dace are much less abundant than they used to be and are probably declining. There are, however, no historic estimates of abundance nor have there been any recent surveys. In fact, there have been reports of the dace since Williams et al. (1982).

Description:

Speckled dace are small cyprinids, usually measuring less than 8 cm SL at maturity but occasionally reaching 11 cm SL (Moyle 2002). Although physically variable, they are characterized by a wide caudal peduncle, small scales (47-89 along lateral line), and pointed snout with a small subterminal mouth. At maturity the dorsal fin usually has 8 rays and originates well behind the origin of the pelvic fins (Moyle 2002). The anal fin has 6-8 rays. Pharyngeal teeth (1,4-4,1 or 2,4-4,2) are significantly curved with a minor grinding surface. The maxilla usually has a small barbel at each end. The snout is connected to the upper lip (premaxilla) by a small bridge of skin (frenum). As their common name indicates, most fish larger than 3 cm have distinctive dark speckles on the upper and sides of the body, although some fish from highly turbid waters may lack speckles. Dark blotches present on the side can merge creating what looks like a dark lateral band. A stripe on the head, below the eye, extends to the snout, and there is black a spot on the caudal peduncle. The rest of the body is dusky yellow to olive, with the belly being a paler color. Breeding adults of both sexes have fins tipped by orange or red, while males also have red snouts and lips, and tubercles on the head and pectoral fins.

The speckled dace has long been considered the most widely distributed species in the western United States and isolated populations can be found in many small streams and springs. However, its taxonomy is poorly understood and highly confusing because the species is naturally so variable. Originally, small morphological differences among speckled dace populations isolated in different watersheds (especially in the endorheic valleys of the Great Basin) led ichthyologists to describe 12 separate species (Jordan and Evermann 1896). Later, because of the plastic morphology of the species, all speckled dace were collapsed into a single species, Rhinichthys osculus (Hubbs et al. 1974). Recently, however, genetic analysis has supported a return to the some of the original taxonomy. A number of forms are now recognized as separate taxa not only because of their distinctive morphology, different habitats, and isolation from other dace populations but also because they can be shown to be genetically distinct. Four such forms are now recognized in the Death Valley system: the Owens speckled dace, the Long Valley speckled dace, the Amargosa Canyon speckled dace, and the Ash Meadows speckled dace.
Gilbert (1893) described Rhinichthys nevadensis from Ash Meadows, Nevada, but the subspecific name R. o. nevadensis was later also applied to speckled dace in the Amargosa River canyon and Owens Basin (La Rivers 1962, Moyle 2002). However, in the early 1980s research revealed that these three populations are distinct (Williams et al. 1982). The Amargosa fish are characterized by a comparatively smaller head depth, shorter snout-to-nostril length, longer anal-to-caudal length, more pectoral fin rays, and fewer vertebrae than the other forms. As a consequence, Williams et al. (1982) and Deacon and Williams (1984) recommended that the populations from the three areas be placed in separate subspecies. More recently, the dace population in Long Valley in the northern Owens Basin were found to be morphologically distinct and genetically monophyletic (Sada 1989, 1995; Oakey 2004).
In a way, the taxonomic confusion generated by this plastic species is of little consequence because all the populations in the Amargosa River drainage and Owens River drainage are in need of protection to prevent their extinction. Thus, it may be convenient for conservation purposes to continue to consider the existing, formal recognition of all three forms as being one taxon, R.o. nevadensis, but recognizing that the three distinct types of dace within the taxon are in more danger of extinction individually than the entire group is collectively.

Taxonomic Unit:

subspecies

Ratings

Major Dam Rating:

N/A

Agriculture Rating:

med

Agriculture Explanation:

Water withdrawals in the Pahrump Valley are the greatest threats to Amargosa aquatic ecosystems

Grazing Rating:

med

Grazing Explanation:

Livestock are still grazed in the area

Rural Rating:

low

Rural Explanation:

Water withdrawals (see agriculture)

Urbanization Rating:

high

Urbanization Explanation:

Water withdrawals (see agriculture)

Instream Mining Rating:

low

Mining Rating :

low

Mining Explanation:

No known effects but present throughout region

Estuarine Alteration Rating:

N/A

Transportation Rating:

low

Transportation Explanation:

Roads go along or cross the river in a number of places

Logging Rating:

N/A

Fire Rating:

med

Fire Explanation:

Fire can affect riparian habitats in rare years

Recreation Rating:

med

Recreation Explanation:

Recreational use in the region is fairly high, including off-road vehicle use.

Harvest Rating :

N/A

Hatcheries Rating:

N/A

Alien Species Rating:

high

Alien Species Explanation:

Competition/predation from mosquitofish is likely major reason for species decline

Scores

Distribution Score:

1

Area Occupied Score:

1

Area Occupied Justification:

Endemic to Amargosa Canyon

Pop Size Score:

2

Pop Size Justification:

Small and fluctuating; no good census exists

Intervention Dependence Score:

2

Intervention Dependence Justification:

Refuge populations must be established

Tolerance Score:

2

Tolerance Justification:

Fairly narrow requirements within the river

Genetic Risk Score:

1

Genetic Risk Justification:

Small isolated populations

Climate Change Score :

1

Climate Change Justification:

Water withdrawals likely to increase in warming climate

Threats Score :

2

Threats Justification:

See Table 1.

Certainty:

3

Certainty Justification:

No recent data

Other Information

Threats:

The major threat to the Amargosa Canyon speckled dace is the potential dewatering of its unique habitats, the Amargosa River and tributaries, combined with interactions with invasive species (Table 1).
Agriculture, rural residential development, urbanization. These three categories of threat are lumped together because together they result in by water withdrawals from both distant and near points on the aquifer that feeds the Amargosa River. The Amargosa Aquifer supplies the springs of Ash Meadows, Nevada, and the Amargosa River to which they are tributary (Riggs and Deacon 2002). It receives much of its recharge flow from areas on the northern and northeastern slopes of the nearby Spring Mountains but, along with springs on the eastern side of Death Valley, is partially dependent on regional groundwater movement through large, ancient aquifers that extend into western Utah and central Nevada (Dettinger et al.1995, Deacon et al. 2007). In order to slake the ever-thirsty city of Las Vegas, the Southern Nevada Water Authority (SNWA) proposed to mine large quantities of this water from several different valleys which lie within the Ash Meadows groundwater basin (Breen 2004, Southern Nevada Water Authority 2004, Vogel 2004). At the present time, farming operations and human settlements in the Amargosa region are withdrawing increasing amounts of water from the aquifer and groundwater pumping from the regional aquifer already is producing declines in water stored in the aquifer, noticeable as in the decline of the water level of the closely-monitored Devils Hole, Nevada (habitat of the endangered Devil's Hole pupfish, Cyprinodon diabolis) (Riggs and Deacon 2002, Bedinger and Harrill 2006). If the Amargosa region water withdrawals continue to increase and if Las Vegas proceeds with its planned withdrawals, it is highly likely that the Amargosa River will have its flows greatly reduced or even disappear completely during dry years. Already, diversions of springs and outflows on private land in the Tecopa area have reduced local flows in the river and local pupfish populations as well. With an increasing human population in Tecopa and the upper Amargosa Valley, demand for water and protection from floods is increasing. The latter can result in channelization of sections of the river.
Although most land in the Amargosa Canyon is owned by The Nature Conservancy or the Bureau of Land Management, critical habitat for the dace includes a large tract of privately owned land, China Ranch. This ranch contains the headwater area of Willow Creek. Diversion of water from the creek or other alterations affecting water quality could cause dace populations to decline further.
Grazing. While water is diverted from the stream directly for cattle and pumped to grow alfalfa, there are enough cows scattered through the dace region to affect streambanks and riparian vegetation, at least locally. Cows tend to concentrate around water to their effects can be disproportionate to their actual numbers.
Recreation. The deserts of California receive high recreational use, especially from people coming from the urban areas of the southern California. Much of this recreation is focused on vehicular use, both off-road and on the hundreds of old mining and other roads that lace the landscape. Such use is hard to regulate, much less keep track of, so even though rules are in place banning use of off-road vehicles from sensitive areas, destruction of riparian and streambed habitat by recreational users still happens. This is always a threat to the Amargosa River and its watershed.
Alien species. A more immediate threat to the dace is the presence of alien fish species in the quiet-water habitat it prefers. In particular, western mosquitofish may be reducing its numbers through competition and predation. The presence of large numbers of mosquitofish, which are omnivorous like the dace, indicates they are consuming resources otherwise available to the dace. Because much of its habitat is on public land, additional introductions of undesirable species that may affect dace populations are possible.

Threat Caption:

Major anthropogenic factors limiting, or potentially limiting viability of Amargosa Canyon speckled dace populations in California, where a factor rated high is a major limiting factor, a factor rated intermediate is a factor that has the potential to be a major limiting factor but has had only a moderate effect so far on population viability, and a factor rated low has a low or unknown effect on population viability. Certainty of these judgments is intermediate.

Climate Effects:

As one might expect of a desert species, climate change poses a direct threat to the continued existence of Amargosa Canyon speckled dace. Isolated desert springs and rivers fed by subsurface flow systems are precarious ecosystems, vulnerable to geologic and anthropogenic disruption. Fed by rain and snow melt at high elevation in the desert mountain ranges (Riggs and Deacon 2002), desert aquifers in the Death Valley region will likely receive less recharge as the region warms. This decline in regional water supply will be compounded by the growing human demand for water in southern Nevada which will only increase as the climate gets hotter and more arid.

Metrics Caption:

Metrics for determining the status of Amargosa Canyon speckled dace, where 1 is a major negative factor contributing to status, 5 is a factor with no or positive effects on status, and 2-4 are intermediate values. See Introduction for further explanation.

Management Recommendation:

The Amargosa Canyon speckled dace needs immediate attention in order to keep from disappearing.
1. Populations must be resurveyed as soon possible to determine if the Amargosa Canyon speckled dace is still extant. If it is, populations should monitored annually thereafter. The BLM placed high priority on Amargosa Canyon fish surveys in its 2006 Implementation Plan for the Amargosa Desert Area of Critical Environmental Concern Report, but has been unable to fund any such survey to this date.
2. Efforts should be made to ensure a natural flow of water in Willow Creek and the Amargosa River, including flood flows that reduce populations of alien fishes. Fortunately, most of the canyon area is now owned by The Nature Conservancy and the Bureau of Land Management. Amargosa Canyon is part of a BLM Area of Critical Environmental Concern and is closed to off-road vehicle use. Fences and barriers need to be properly maintained, however, because vehicle trespass has a common problem in the past.
3. In Willow Creek, an evaluation should be conducted to see if permanent eradication of alien species from speckled dace habitat is possible. If it is not, invasion-proof refuges for the species (and Amargosa pupfish) should be created in the drainage.
4. The small population of dace in the Amargosa River may be dependent upon recruitment of dace from Willow Creek. If this is so, maintenance of adequate flows from China Ranch are critical to the survival of this subspecies.
5. Efforts also should be made to locate the spring occupied by dace in 1937 (Miller 1938) to determine if this spring, or another nearby spring, could again support a dace population. As discussed for Amargosa pupfish, frequent surveys of Amargosa Canyon are necessary to monitor habitat conditions and the presence of alien fishes.
6. The most difficult problem is water removal from the aquifer that apparently feeds the river. The U.S. Supreme Court decision that protected the Devils Hole pupfish from water withdrawals (United States v. Cappaert 1977) may be some help here, but its application on a larger, regional basis is uncertain. Listing of the dace and other regional fishes under the ESA might forestall massive groundwater pumping by the Southern Nevada Water District until it can be determined that the Amargosa River depends on the aquifer and would be threatened by the pumping. Protection of the fishes thus could protect an entire unique desert ecosystem

Score = 1. The Amargosa Canyon speckled dace is Bureau of Land management sensitive species and is listed as critically imperiled (G5T1S1) by Natureserve (Natureserve.com) and Endangered by the American Fisheries Society (Jelks et al. 2008). It apparently has not been seen since 1982, so could already be extinct.